An Improved Guess-and-Determine Attack on the A5/1 Stream Cipher

Ayan Mahalanobis, Jay Shah

Abstract

In Europe and North America, the most widely used stream cipher to ensure privacy and confidentiality of conversations in GSM mobile phones is the A5/1. In this paper, we present an improved guess-and-determine attack on the A5/1 stream cipher with an average time complexity of 2^48.5, which is much less than any known guess-and-determine attack. The attack has a 100% success rate and requires a small amount of memory. We provide a detailed description of our new attack along with its implementation results.

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